Tamron couldn't stay behind in the 70-300 race, and also will trump Sigma in specs. Where Sigma refused to put the HSM drive in besides the OS, Tamron will even put in an USD (ultrasonic silent drive) focus motor in the lens. I am curious how this lens will turn out to be in performance, so far the specs, VC and USD, sound like a true Nikon/Canon alternative.
Let's hope the SP on the lens is like the SP on the macro 90mm and truly means Superior Performance.

Ooh, very interesting. Have a link to the announcement to save others looking for it.

I haven't seen detailed reviews on the Sigma 70-300 OS yet, but it isn't an EX designated lens. The Tamron is SP, so while it should be better, it'll likely be more expensive too. So as always, price vs performance will be key, as the Canon 70-300 IS USM and Sony 70-300G SSM are already excellent lenses in that range, I think to beat it optically will be too big a challenge so they will have to compete on price.

Most interesting is Tamron's USD, this is the first I heard of it. It is certainly the biggest weakness of Tamrons, and once they roll that out into their lineup particularly on the higher end, I think they will be much more attractive.

Yeah, looks quite similar to the Nikkor from the outside!
And even the number of lenses and lens-groups is identical: "Elements/Groups: 17/12"
But this will be the real challenge for Tamron: banging 17 lenses together and still have good contrast, low flare and precise assembly for good centering.

Good news for those who like a little variety in their lens shopping options. The price is looking reallllly good at $449 USD. I think it'll be a good performer too, given Tamron's track record lately.